Discovery of “dancing” galaxies gives astronomers vital clues in black hole mystery

Astronomers hope to solve the mystery of black hole formation by observing how galaxies interacted at the Cosmic Dawn.

There are more mysteries hidden in the universe than we could possibly imagine. One that’s been confounding astronomers for years is the formation of black holes and the highly illuminant disks, known as quasars, surrounding them. These spatial formations shine brighter than an entire galaxy and continue to puzzle astronomers.

Large galaxies, including our own Milky Way, contain supermassive black holes at their centers, known for their capacity to absorb matter. The friction generated while sucking in gas and dust from their surroundings creates a disk containing vast amounts of energy.

When a black hole actively consumes matter, it’s referred to as being in the quasar phase, which could last a few million years. The intense radiation emitted by quasars affects the star formation in galaxies. It can heat the surrounding gas to such high temperatures that it can't cool down enough to collapse and form new stars, slowing down the galaxy's growth.

It’s also known that galaxies hosting quasars frequently undergo bursts of star formation, generating hundreds to thousands of times the mass of our Sun in new stars each year.

Astronomers need to study galaxies and black holes before they merge and become bright quasars to understand how they formed in the early universe. However, research has been slow because these space objects are very faint and hard to detect.

Dancing to form a monster galaxy

A widely accepted theory is that when gas-rich galaxies merge to form a single larger galaxy, the gravitational interaction causes gas to fall toward the supermassive black hole in one or both of the galaxies, causing quasar activity.

To address this challenge, a team of international researchers, led by Associate Professor Yoshiki Matsuoka of Ehime University, used the Subaru Telescope’s Hyper Suprime-Cam to detect two very faint quasars – about 10 to 100 times dimmer than typical high-luminosity quasars.

The cosmic objects were located approximately 12.8 billion light-years away from us, in the direction of the Virgo constellation. This pair of quasars existed during the first 900 million years of the Universe, dating back to the “Cosmic Dawn” era.

The scientists used the ALMA (Atacama Large Millimeter/Submillimeter Array) radio telescope to further investigate the quasars and determine whether the galaxies were going to merge.

The ALMA observations mapped the quasars of the host galaxies and showed that they were linked by a "bridge" of gas and dust. This indicates that the two galaxies are, in fact, merging.

“When we first observed the interaction between these two galaxies, it was like watching a dance, with the black holes at their centers having started their growth. It was truly beautiful,” Professor Takuma Izumi said about the discovery.

The ALMA observations enabled the team to measure the amount of gas available for new star formation. They discovered that both galaxies are highly enriched in gas, indicating that, along with increased quasar activity in the future, the merger will likely trigger a rapid surge in star formation, or "starburst."

This combination of intense starburst and quasar activity is expected to result in one of the brightest types of objects in the Universe, often referred to as a "monster galaxy."

Deconstructing the mysteries of the universe

The research's results are important for understanding the early evolution of galaxies and black holes in the early Universe. The joint powers of Subaru Telescope and ALMA have started the process of unveiling the nature of supermassive black holes and the gas in the host galaxies.

While the properties of the stars in the host galaxies remain unknown, scientists can learn about the stellar properties of these space objects using the James Webb Space Telescope.

“As these are the long-sought ancestors of high-luminosity quasars, which should serve as a precious cosmic laboratory, I hope to deepen our understanding of their nature and evolution through various observations in the future,” Professor Izumi concluded.